1. Field of the Invention
This invention relates to resolvers and synchros and more particularly to a brushless printed circuit resolver operating by capacitive coupling.
2. Description of the Prior Art
Various prior art patents utilize capacitive coupling for providing an indication of the rotor angle. However, most of these patents require either a physical electrical connection to the rotor, or use an insulating or conducting member disposed between two stationary members, which as it rotates changes the capacitive coupling between the stationary members. Exemplary of prior art patents are:
U.S. Pat. No. 2,534,505 issued Dec. 19, 1950 to W. K. Ergen which teaches a dielectric vane rotated between a plate and segments of a plate to vary capacitance therebetween. The Ergen patent requires a rather complicated bridge for an indication pickup.
U.S. Pat. No. 2,614,171 issued Oct. 14, 1952 to L. Fein teaches an electrical apparatus for measuring angles which requires an electrical connection to the rotor for operation. The device disclosed in Fein is effected in operation by the distributed resistance of the elements being used.
U.S. Pat. No. 2,674,729 issued Apr. 6, 1954 to E. P. Carter teaches a measuring apparatus requiring slip ring connections to the rotary member. The stator and rotor are each of the same type of construction.
U.S. Pat. No. 3,198,937 issued Aug. 3, 1965 to A. M. Wooster teaches a digital position-indicating unit. The unit disclosed therein provides a pulsetrain output.
U.S. Pat. No. 3,221,256 issued Nov. 30, 1965 to R. L. Walden teaches an electrostatic position transducer. The device disclosed therein is a single phase device requiring an electrical connection to the movable member. Walden does not teach a device providing a quadrature or polyphase output.
U.S. Pat. No. 3,517,282 issued June 23, 1970 to A. Miller teaches a variable capacitance transducer which utilizes a dielectric plate rotatable between spaced apart capacitor plates for providing position information. The device disclosed does not provide a quadrature output.
U.S. Pat. No. 3,668,672 issued June 6, 1972 to J. A. Parnell teaches a capacitive transducer utilizing shielding plate disposed between two capacitive coupled outer plates. The shielding plate is movable and has an electrical connection through a slip ring made thereto. The Parnell device provides only a single phase output.
U.S. Pat. No. 3,732,553 issued May 8, 1973 to E. V. Hardway, Jr. discloses a capacitive pick-off transducer using a movable shield plate disposed between capacitive plates to vary capacitance. A connection is required to the movable shield plate to maintain it at a ground potential level. Hardway does not teach a quadrature related output.
U.S. Pat. No. 3,845,377 issued Oct. 29, 1974 to A. Shimotori teaches a rotational angle transducer for producing a pulse output. A rotatable shield disposed between capacitively coupled members is utilized for developing the desired output.
U.S. Pat. No. 3,961,318 to R. W. Farrand teaches an Electrostatic Position Measuring Transducer in which two spaced relatively movable elements have electrostatically coupled sets of uniformly spaced interdigitated finger electrodes to form a precision, high gain linear or angular position measuring transducer. Each element has two base portions with a plurality of finger portions extending therefrom. The finger portions on each element are uniformly spaced one measurement cycle apart, with the fingers of one base portion interdigitated at one half cycle spacing with the fingers of the other base portion. No direct electrical connections are made to the movable elements which is connected to the instrumented member. The fingers on the movable and stationary member are of the same general shape, with the stationary fingers being slightly smaller radially. The teaching of this patent seems mainly to be directed to a resolver having a rather large number of poles.
A problem with prior art capactively coupled resolvers is that they have difficulty in providing a good output position signal with little undesirable harmonics.
Prior art capacitively coupled resolvers are generally operable with a relatively large number of cycles per revolution and it is difficult to obtain a good output from a device having a small number of cycles per revolution.